1. Field of the Invention
The present invention pertains to optical pulse stretchers, and, more particularly, to an optical pulse stretcher etalon.
2. Description of the Related Art
The increasing power and speed of many types of electronic systems has focused attention on optical technologies. Optical technologies are attractive for a variety of reasons that may vary depending on the type of technology. However, desirable characteristics typically include generally faster transmission and higher bandwidth of optical signals relative to electrical signals. Information is typically conveyed in optical signals in a series of light pulses, or “optical pulse trains.” Frequently, although not always, the optical pulses convey information digitally in 0's and 1's just as electrical pulses in electrical signals do.
Optical technologies are nevertheless not without their own problems. One problem arises from the fleeting nature of the light pulses. Demanding applications employ light pulses of very short duration, e.g., 1 ns or 1 ps, and future increases in capabilities are expected to push pulse widths even lower. Although the signals in optical systems are light pulses, the optical systems themselves employ opto-electronic components that are partly optical and partly electronic. Pulse widths of the magnitudes contemplated herein are difficult for the electronic side of the opto-electronic components to process in a timely fashion.
One solution to this dilemma is to “stretch” the light pulses. One common type of pulse stretcher is the “etalon.” An etalon is basically a cavity bounded by two reflective surfaces. One surface is essentially completely reflective, e.g., a mirror. The other surface is partially reflective, i.e., part of the optical signal will reflect off the surface while a portion of the optical signal propagates through the surface. Thus, an optical signal is introduced into the cavity and impinges upon the partially reflective surface first. A portion of the optical signal propagates through the partially reflective surface. A portion also reflects off the partially reflective surface to the fully reflective surface, which then again reflects from the fully reflective portion. The twice reflected portion then impinges upon the partially reflective surface, whereupon the process repeats. The pulse portions propagating through the partially reflective surface are then collected and combined to create a “composite” pulse.
This “composite” pulse is “stretched,” i.e., of longer duration than the “base” pulse that was originally directed into the etalon. This technique admirably produces wider, i.e., longer duration, pulses. The stretched pulses are easier for the electrical part of the opto-electronic components to handle and process. However, several drawbacks accompany these pulse stretching techniques.
One significant problem is information loss. For instance, the width of the pulse might carry certain information that can be useful. The spacing of the reflective surfaces in conventional etalons, however, is driven by considerations such as volume and size, as opposed to any characteristic of the light pulses. The characteristics of the resultant stretched pulse bear no relationship to the characteristics of the base pulse from which such information can be retrieved. Thus, meaningful information that may be conveyed by the width of the base pulse is lost.
Another significant problem impacts the detector that processes that stretched pulses. The stretched pulse typically presents abrupt changes in intensity levels, e.g. from “off” to “on,” with very short transition periods. These abrupt transitions can generate a phenomenon known as “ringing” in the detector's electronics. The detector's electronics consequently must be designed to deal with this phenomenon, which complicates the electronics and can increase the space needed for the electronics within the optical system. Complexity is generally proportional to the rate of failure. In some high performance applications, space is at a premium. The need to compensate for ringing can therefore be highly undesirable in some applications.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.